This document describes known methods of flashing BIOS on Lenovo ThinkPads without external programmer. The main goal is flashing coreboot while running stock BIOS, but it may be used for flashing modified vendor BIOS as well.

Table of Contents

• Ivy Bridge series (X230, T430, etc.)
  • Introduction
  • Requirements
  • BIOS versions
  • Downgrading BIOS
    • Enabling UEFI mode
  • Examining protections (theory)
  • Creating a backup
    • Restoring
  • Removing protections (practice)
  • About Intel ME
• Sandy Bridge series (X220, T420, etc.): WIP
• Penryn and Nehalem series (X200, T400, X201, T410, etc.): WIP
• Common methods
  • HDA_SDO/GPIO33
• Credits
• License

Ivy Bridge series (X230, T430, etc.)

A guide for Ivy Bridge ThinkPads has also been merged to coreboot documentation, see here.

Old versions of stock BIOS for these models have several security issues. In context of this guide, two of them are of interest.

First is the fact the SMM_BWP and BLE are not enabled in BIOS versions released before 2014. I have tested many versions on T430 and X230 and found out that SMM_BWP=1 only since the update, the changelog of which contains following line:

(New) Improved the UEFI BIOS security feature.

Second is S3 Boot Script vulnerability, that was discovered and fixed later.

Requirements

• USB drive (in case you need to downgrade BIOS). There were reports that GPT-partitioned drive didn't work and the fix was to change partition table to MBR.
• Linux install that (can be) loaded in UEFI mode.
• CHIPSEC
• Recent flashrom. At least version 1.0 is required, older versions of flashrom do not have --ifd option. (Workaround by using layout file is possible, but it's more complicated.)
• iomem=relaxed kernel parameter for using internal programmer.

BIOS versions

Below is a table of BIOS versions that are vulnerable enough for our goals, per model. The version number means that you need to downgrade to that or earlier version.

If your BIOS version is equal or lower, skip to the Examining protections section. If not, go through the downgrade process, described next.

Downgrading BIOS

Go to the Lenovo web site and download BIOS Update Bootable CD for your machine of needed version (see above).

Lenovo states that BIOS has "security rollback prevention", meaning once you update it to some version X, you will not be able to downgrade it to pre-X version. That's not true. It seems that this is completely client-side restriction in flashing utilities (both Windows utility and Bootable CD). You just need to call winflash.exe or dosflash.exe directly. Therefore you need to modify the bootable CD image you just downloaded.

Extract an El Torito image:

geteltorito -o ./bios.img g1uj41us.iso

Mount the partition in that image:

sudo mount -t vfat ./bios.img /mnt -o loop,offset=16384

List files, find the AUTOEXEC.BAT file and the FLASH directory:

ls /mnt
ls /mnt/FLASH

Inside the FLASH directory, there should be a directory called G1ET93WW or similar (exact name depends on your ThinkPad model). See what's inside:

ls /mnt/FLASH/G1ET93WW

There must be a file with .FL1 extension called $01D2000.FL1 or something similar.

Now open the AUTOEXEC.BAT file:

sudo vim /mnt/AUTOEXEC.BAT

You will see a list of commands:

@ECHO OFF
PROMPT $p$g
cd c:\flash
command.com

Replace the last line (command.com) with this (change path to the .FL1 file according to yours):

dosflash.exe /sd /file G1ET93WW\$01D2000.FL1

Save the file, then unmount the partition:

sudo umount /mnt

Write this image to a USB drive (replace /dev/sdX with your USB drive device name):

sudo dd if=./bios.img of=/dev/sdX bs=1M

Now reboot and press F1 to enter BIOS settings. Open the Startup tab and set the startup mode to Legacy (or Both/Legacy First):

Press F10 to save changes and reboot.

Now, before you process, make sure that AC adapter is connected! If your battery will die during the process, you'll likely need external programmer to recover.

Boot from the USB drive (press F12 to select boot device), and BIOS flashing process should begin:

It may reboot a couple of times in the process. Do not interrupt it.

Enabling UEFI mode

When downgrade is completed, go back to the BIOS settings and set startup mode to UEFI (or Both/UEFI First). This is required for vulnerability exploitation.

Then boot to your system and make sure that /sys/firmware/efi or /sys/firmware/efivars exist.

Examining protections (theory)

There are two main ways that Intel platform provides to protect BIOS chip:

• BIOS_CNTL register of LPC Interface Bridge Registers (accessible via PCI configuration space, offset 0xDC). It has:

  • SMM_BWP (SMM BIOS Write Protect) bit. If set to 1, the BIOS is writable only in SMM. Once set to 1, cannot be changed anymore.
  • BLE (BIOS Lock Enable) bit. If set to 1, setting BIOSWE to 1 will raise SMI. Once set to 1, cannot be changed anymore.
  • BIOSWE (BIOS Write Enable) bit. Controls whether BIOS is writable. This bit is always R/W.

• SPI Protected Range Registers (PR0-PR4) of SPI Configuration Registers (SPIBAR+0x74 - SPIBAR+0x84). Each register has bits that define protected range, plus WP bit, that defines whether write protection is enabled.

  There's also FLOCKDN bit of HSFS register (SPIBAR+0x04) of SPI Configuration Registers. When set to 1, PR0-PR4 registers cannot be written. Once set to 1, cannot be changed anymore.

To be able to flash, we need SMM_BWP=0, BIOSWE=1, BLE=0, FLOCKDN=0 or SPI protected ranges (PRx) to have a WP bit set to 0.

Let's see what we have. Make sure that you have enabled and booted in UEFI mode, then examine HSFS register:

sudo chipsec_main -m chipsec.modules.common.spi_lock

You should see that FLOCKDN=1:

[x][ =======================================================================
[x][ Module: SPI Flash Controller Configuration Locks
[x][ =======================================================================
[*] HSFS = 0xE009 << Hardware Sequencing Flash Status Register (SPIBAR + 0x4)
    [00] FDONE            = 1 << Flash Cycle Done
    [01] FCERR            = 0 << Flash Cycle Error
    [02] AEL              = 0 << Access Error Log
    [03] BERASE           = 1 << Block/Sector Erase Size
    [05] SCIP             = 0 << SPI cycle in progress
    [13] FDOPSS           = 1 << Flash Descriptor Override Pin-Strap Status
    [14] FDV              = 1 << Flash Descriptor Valid
    [15] FLOCKDN          = 1 << Flash Configuration Lock-Down

Then check BIOS_CNTL and PR0-PR4:

sudo chipsec_main -m common.bios_wp

Good news: on old BIOS versions, SMM_BWP=0 and BLE=0.

Bad news: there are 4 write protected SPI ranges:

[x][ =======================================================================
[x][ Module: BIOS Region Write Protection
[x][ =======================================================================
[*] BC = 0x 8 << BIOS Control (b:d.f 00:31.0 + 0xDC)
    [00] BIOSWE           = 0 << BIOS Write Enable
    [01] BLE              = 0 << BIOS Lock Enable
    [02] SRC              = 2 << SPI Read Configuration
    [04] TSS              = 0 << Top Swap Status
    [05] SMM_BWP          = 0 << SMM BIOS Write Protection
[-] BIOS region write protection is disabled!

[*] BIOS Region: Base = 0x00500000, Limit = 0x00BFFFFF
SPI Protected Ranges
------------------------------------------------------------
PRx (offset) | Value    | Base     | Limit    | WP? | RP?
------------------------------------------------------------
PR0 (74)     | 00000000 | 00000000 | 00000000 | 0   | 0
PR1 (78)     | 8BFF0B40 | 00B40000 | 00BFFFFF | 1   | 0
PR2 (7C)     | 8B100B10 | 00B10000 | 00B10FFF | 1   | 0
PR3 (80)     | 8ADE0AD0 | 00AD0000 | 00ADEFFF | 1   | 0
PR4 (84)     | 8AAF0800 | 00800000 | 00AAFFFF | 1   | 0

Other way to examine SPI configuration registers is to just dump SPIBAR:

sudo chipsec_util mmio dump SPIBAR

You will see SPIBAR address (0xFED1F800) and registers (for example, 00000004 is HSFS):

[mmio] MMIO register range [0x00000000FED1F800:0x00000000FED1F800+00000200]:
+00000000: 0BFF0500
+00000004: 0004E009
...

As you can see, the only thing we need is to unset WP bit on PR0-PR4. But that cannot be done once FLOCKDN is set to 1.

Now the fun part!

FLOCKDN may only be cleared by a hardware reset, which includes S3 state. On S3 resume boot path, the chipset configuration has to be restored and it's done by executing so-called S3 Boot Scripts. You can dump these scripts by executing:

sudo chipsec_util uefi s3bootscript

There are many entries. Along them, you can find instructions to write to HSFS (remember, we know that SPIBAR is 0xFED1F800):

Entry at offset 0x2B8F (len = 0x17, header len = 0x0):
Data:
02 00 17 02 00 00 00 01 00 00 00 04 f8 d1 fe 00 |
00 00 00 09 e0 04 00                            |
Decoded:
  Opcode : S3_BOOTSCRIPT_MEM_WRITE (0x0002)
  Width  : 0x02 (4 bytes)
  Address: 0xFED1F804
  Count  : 0x1
  Values : 0x0004E009

These scripts are stored in memory. The vulnerability is that we can overwrite this memory, change these instructions and they will be executed on S3 resume. Once we patch that instruction to not set FLOCKDN bit, we will be able to write to PR0-PR4 registers.

Creating a backup

Before you proceed, please create a backup of the bios region. Then, in case something goes wrong, you'll be able to flash it back externally.

The me region is locked due to active ME, so an attempt to create a full dump will fail. But you can back up the bios:

sudo flashrom -p internal -r bios_backup.rom --ifd -i bios

Restoring

If you will even need to flash it back, use --ifd -i bios as well:

sudo flashrom -p <YOUR_PROGRAMMER> -w bios_backup.rom --ifd -i bios

Important: if you will omit --ifd -i bios for flashing, you will brick your machine, because your backup has FFs in place of fd and me regions. Flash only bios region!

Removing protections (practice)

The original boot script writes 0xE009 to HSFS. FLOCKDN is 15th bit, so let's write 0x6009 instead:

Run this:

sudo chipsec_main -m tools.uefi.s3script_modify -a replace_op,mmio_wr,0xFED1F804,0x6009,0x2

You will get a lot of output and in the end you should see something like this:

[*] Modifying S3 boot script entry at address 0x00000000DAF49B8F..
[mem] 0x00000000DAF49B8F
[*] Original entry:
 2  0 17  2  0  0  0  1  0  0  0  4 f8 d1 fe  0 |
 0  0  0  9 e0  4  0                            |
[mem] buffer len = 0x17 to PA = 0x00000000DAF49B8F
 2  0 17  2  0  0  0  1  0  0  0  4 f8 d1 fe  0 |
 0  0  0  9 60  0  0                            |     `
[mem] 0x00000000DAF49B8F
[*] Modified entry:
 2  0 17  2  0  0  0  1  0  0  0  4 f8 d1 fe  0 |
 0  0  0  9 60  0  0                            |     `
[*] After sleep/resume, check the value of register 0xFED1F804 is 0x6009
[+] PASSED: The script has been modified. Go to sleep..

Now go to S3, then resume and check FLOCKDN. It should be 0:

sudo chipsec_main -m chipsec.modules.common.spi_lock

...
[x][ =======================================================================
[x][ Module: SPI Flash Controller Configuration Locks
[x][ =======================================================================
[*] HSFS = 0x6008 << Hardware Sequencing Flash Status Register (SPIBAR + 0x4)
    [00] FDONE            = 0 << Flash Cycle Done
    [01] FCERR            = 0 << Flash Cycle Error
    [02] AEL              = 0 << Access Error Log
    [03] BERASE           = 1 << Block/Sector Erase Size
    [05] SCIP             = 0 << SPI cycle in progress
    [13] FDOPSS           = 1 << Flash Descriptor Override Pin-Strap Status
    [14] FDV              = 1 << Flash Descriptor Valid
    [15] FLOCKDN          = 0 << Flash Configuration Lock-Down
[-] SPI Flash Controller configuration is not locked
[-] FAILED: SPI Flash Controller not locked correctly.
...

Set BIOSWE:

sudo setpci -s 00:1f.0 dc.b=09

Remove WP from protected ranges:

sudo chipsec_util mmio write SPIBAR 0x74 0x4 0xAAF0800
sudo chipsec_util mmio write SPIBAR 0x78 0x4 0xADE0AD0
sudo chipsec_util mmio write SPIBAR 0x7C 0x4 0xB100B10
sudo chipsec_util mmio write SPIBAR 0x80 0x4 0xBFF0B40

Verify that it worked:

sudo chipsec_main -m common.bios_wp

[x][ =======================================================================
[x][ Module: BIOS Region Write Protection
[x][ =======================================================================
[*] BC = 0x 9 << BIOS Control (b:d.f 00:31.0 + 0xDC)
    [00] BIOSWE           = 1 << BIOS Write Enable
    [01] BLE              = 0 << BIOS Lock Enable
    [02] SRC              = 2 << SPI Read Configuration
    [04] TSS              = 0 << Top Swap Status
    [05] SMM_BWP          = 0 << SMM BIOS Write Protection
[-] BIOS region write protection is disabled!

[*] BIOS Region: Base = 0x00500000, Limit = 0x00BFFFFF
SPI Protected Ranges
------------------------------------------------------------
PRx (offset) | Value    | Base     | Limit    | WP? | RP?
------------------------------------------------------------
PR0 (74)     | 0AAF0800 | 00800000 | 00AAF000 | 0   | 0
PR1 (78)     | 0ADE0AD0 | 00AD0000 | 00ADE000 | 0   | 0
PR2 (7C)     | 0B100B10 | 00B10000 | 00B10000 | 0   | 0
PR3 (80)     | 0BFF0B40 | 00B40000 | 00BFF000 | 0   | 0
PR4 (84)     | 00000000 | 00000000 | 00000000 | 0   | 0

Bingo!

Now you can flash coreboot (or anything else) with flashrom.

Remember to flash only bios region (use --ifd -i bios -N). fd and me are still not writable.

Note: if you're flashing coreboot for the first time, you should have an external SPI programmer just in case. It will help you recover if you flash non-working ROM.

About Intel ME

Unlocking PRx doesn't allow you to flash ME or Flash Descriptor, so you cannot use me_cleaner. Both me and fd regions will still be write-protected even if you flash coreboot. For now, the best way to get rid of ME is to flash me_cleaned firmware externally.

As an alternative, you can use Soft Temporary Disable Mode. This is ME's built-in mechanism that BIOS can use to "ask" ME to disable itself on the next boot. In this mode ME doesn't load its kernel and stops at BUP phase. This mode is saved to ME NVRAM and thus preserved between reboots and poweroffs. Working patch for coreboot is available.

Some possible future solutions are described below.

HMRFPO (updated: won't work)

HMRFPO (Host ME Region Flash Protection Override) is a command BIOS can use to unlock ME region on SPI flash for writing. Vendor can disable it during manufacturing. Unfortunately it's disabled on ThinkPads and can't be used.

HDA_SDO (not implemented)

It is possible to make flash descriptor writable for one boot by asserting HDA_SDO pin high on boot. It should be possible to flash unlocked descriptor while in this state, and that should open ability to flash ME afterwards. See here for more info.

Sandy Bridge series (X220, T420, etc.): WIP

S3 Boot Scripts are unprotected on these models too (even on the most recent BIOS versions), but it's not useful, because FLOCKDN and SPI protected ranges are set by LenovoFlashProtectPei UEFI module. It is trivial to patch it, but it resides in protected range, so it can only be flashed externally.

Currently there are no known methods to unlock PRs on these devices internally, but investigation is ongoing.

Penryn and Nehalem series (X200, T400, X201, T410, etc.): WIP

Currently, the only known way to flash these models without external SPI programmer is by using GPIO33. It is not properly documented yet, and no scripts to automate the process were written. There was a success story though: a user from #coreboot/#libreboot IRC channels has successfully corebooted his X201 without touching the SPI chip.

Progress is tracked here.

Common methods

HDA_SDO/GPIO33

There's known Intel "feature", sometimes called "pinmod": you can make flash descriptor writable for one boot by asserting HDA_SDO pin on the motherboard high (on older platforms, you need to assert GPIO33 pin low) at boot time. Writable flash descriptor sometimes allows to flash whole BIOS region using a couple of neat tricks. I will show this using X220 as an example.

This is SPI flash layout on X220:

00000000:00000fff fd
00500000:007fffff bios
00003000:004fffff me
00001000:00002fff gbe

Lenovo BIOS protects, using PR0 register, only small (but critical) part of it: 0x00780000-0x1ffffff.

PR0 defines the end of protected range as 0x1ffffff, but since it's 8MB chip and bios ends at 0x007fffff, 0x00780000-0x007fffff is what actually is protected. This is the last 512K.

As you can see, 0x00500000-0x0077ffff part is totally writable.

Since flash descriptor is writable too, here is what we can do:

• patch flash descriptor:
  • redefine bios as 00500000:0077ffff using ifdtool;
  • define the rest of it (00780000:007fffff) as pd (Platform Data). This is required, otherwise you will not be able to flash it in future;
  • unlock FD and ME regions (ifdtool -u);
• build and flash (small enough) coreboot ROM to this region (must be careful and make sure that reset vector is at the end of our custom region and not at the end of 8MB ROM; use dd or ifdtool for that);
• flash modified descriptor;
• power off (new FD takes effect after cold boot);
• wait a few seconds and power on.

After this, new FD will be in effect and coreboot will be loaded from 0x00500000-0x0077ffff region, instead of Lenovo BIOS. At this point whole 0x00500000-0x007fffff will be writable and you will be able to flash coreboot again or patched vendor BIOS (don't forget to revert fd changes regarding the bios region).

A user from #coreboot/#libreboot IRC channels was able to flash his X201 internally using the idea described above. However, this is not for mass use yet: we need to write scripts to automate the process, locate HDA_SDO or GPIO33 pins on all motherboards in interest, take their photos and explain, what to do with what.

Credits

Rafal Wojtczuk and Corey Kallenberg for discovering the S3 Boot Scripts vulnerability

pgera for the initial research and working solution

Lenovo for fake rollback protection

License

This document is licensed under CC-BY 4.0 terms.